perldelta for overload caching bug fixes

[perl5.git] / pod / perldelta.pod

=encoding utf8

=head1 NAME

[ this is a template for a new perldelta file. Any text flagged as
XXX needs to be processed before release. ]

perldelta - what is new for perl v5.17.0

=head1 DESCRIPTION

This document describes differences between the 5.16.0 release and
the 5.17.0 release.

If you are upgrading from an earlier release such as 5.16.0, first read
L<perl5160delta>, which describes differences between 5.15.0 and
5.16.0.

=head1 Notice

XXX Any important notices here

=head1 Core Enhancements

XXX New core language features go here. Summarise user-visible core language
enhancements. Particularly prominent performance optimisations could go
here, but most should go in the L</Performance Enhancements> section.

[ List each enhancement as a =head2 entry ]

=head1 Security

XXX Any security-related notices go here.  In particular, any security
vulnerabilities closed should be noted here rather than in the
L</Selected Bug Fixes> section.

[ List each security issue as a =head2 entry ]

=head1 Incompatible Changes

XXX For a release on a stable branch, this section aspires to be:

    There are no changes intentionally incompatible with 5.XXX.XXX
    If any exist, they are bugs, and we request that you submit a
    report.  See L</Reporting Bugs> below.

[ List each incompatible change as a =head2 entry ]

=head1 Deprecations

XXX Any deprecated features, syntax, modules etc. should be listed here.
In particular, deprecated modules should be listed here even if they are
listed as an updated module in the L</Modules and Pragmata> section.

[ List each deprecation as a =head2 entry ]

=head1 Performance Enhancements

XXX Changes which enhance performance without changing behaviour go here. There
may well be none in a stable release.

[ List each enhancement as a =item entry ]

=over 4

=item *

XXX

=back

=head1 Modules and Pragmata

XXX All changes to installed files in F<cpan/>, F<dist/>, F<ext/> and F<lib/>
go here.  If Module::CoreList is updated, generate an initial draft of the
following sections using F<Porting/corelist-perldelta.pl>, which prints stub
entries to STDOUT.  Results can be pasted in place of the '=head2' entries
below.  A paragraph summary for important changes should then be added by hand.
In an ideal world, dual-life modules would have a F<Changes> file that could be
cribbed.

[ Within each section, list entries as a =item entry ]

=head2 New Modules and Pragmata

=over 4

=item *

XXX

=back

=head2 Updated Modules and Pragmata

=over 4

=item *

L<File::stat> has been upgraded from version 1.05 to 1.06.

C<File::stat> ignores the L<filetest> pragma, and warns when used in
combination therewith.  But it was not warning for C<-r>.  This has been
fixed [perl #111640].

C<-p> now works, and does not return false for pipes [perl #111638].

=item *

L<Hash::Util> has been upgraded from version 0.11 to 0.12.

C<hash_unlocked> and C<hashref_unlocked> now returns true if the hash is
unlocked, instead of always returning false [perl #112126].

C<hash_unlocked>, C<hashref_unlocked>, C<lock_hash_recurse> and
C<unlock_hash_recurse> are now exportable [perl #112126].

Two new functions, C<hash_locked> and C<hashref_locked>, have been added.
Oddly enough, these two functions were already exported, even though they
did not exist [perl #112126].

=item *

L<Storable> has been upgraded from version 2.34 to 2.35.

Modifying C<$_[0]> within C<STORABLE_freeze> no longer results in crashes
[perl #112358].

=back

=head2 Removed Modules and Pragmata

=over 4

=item *

XXX

=back

=head1 Documentation

XXX Changes to files in F<pod/> go here.  Consider grouping entries by
file and be sure to link to the appropriate page, e.g. L<perlfunc>.

=head2 New Documentation

XXX Changes which create B<new> files in F<pod/> go here.

=head3 L<XXX>

XXX Description of the purpose of the new file here

=head2 Changes to Existing Documentation

XXX Changes which significantly change existing files in F<pod/> go here.
However, any changes to F<pod/perldiag.pod> should go in the L</Diagnostics>
section.

=head3 L<XXX>

=over 4

=item *

XXX Description of the change here

=back

=head1 Diagnostics

The following additions or changes have been made to diagnostic output,
including warnings and fatal error messages.  For the complete list of
diagnostic messages, see L<perldiag>.

XXX New or changed warnings emitted by the core's C<C> code go here. Also
include any changes in L<perldiag> that reconcile it to the C<C> code.

[ Within each section, list entries as a =item entry that links to perldiag,
  e.g.

  =item *

  L<Invalid version object|perldiag/"Invalid version object">
]

=head2 New Diagnostics

XXX Newly added diagnostic messages go here

=head3 New Errors

=over 4

=item *

XXX L<message|perldiag/"message">

=back

=head3 New Warnings

=over 4

=item *

XXX L<message|perldiag/"message">

=back

=head2 Changes to Existing Diagnostics

XXX Changes (i.e. rewording) of diagnostic messages go here

=over 4

=item *

XXX Describe change here

=back

=head1 Utility Changes

XXX Changes to installed programs such as F<perlbug> and F<xsubpp> go
here. Most of these are built within the directories F<utils> and F<x2p>.

[ List utility changes as a =head3 entry for each utility and =item
entries for each change
Use L<XXX> with program names to get proper documentation linking. ]

=head3 L<XXX>

=over 4

=item *

XXX

=back

=head1 Configuration and Compilation

XXX Changes to F<Configure>, F<installperl>, F<installman>, and analogous tools
go here.  Any other changes to the Perl build process should be listed here.
However, any platform-specific changes should be listed in the
L</Platform Support> section, instead.

[ List changes as a =item entry ].

=over 4

=item *

XXX

=back

=head1 Testing

XXX Any significant changes to the testing of a freshly built perl should be
listed here.  Changes which create B<new> files in F<t/> go here as do any
large changes to the testing harness (e.g. when parallel testing was added).
Changes to existing files in F<t/> aren't worth summarising, although the bugs
that they represent may be covered elsewhere.

[ List each test improvement as a =item entry ]

=over 4

=item *

XXX

=back

=head1 Platform Support

XXX Any changes to platform support should be listed in the sections below.

[ Within the sections, list each platform as a =item entry with specific
changes as paragraphs below it. ]

=head2 New Platforms

XXX List any platforms that this version of perl compiles on, that previous
versions did not. These will either be enabled by new files in the F<hints/>
directories, or new subdirectories and F<README> files at the top level of the
source tree.

=over 4

=item XXX-some-platform

XXX

=back

=head2 Discontinued Platforms

XXX List any platforms that this version of perl no longer compiles on.

=over 4

=item XXX-some-platform

XXX

=back

=head2 Platform-Specific Notes

XXX List any changes for specific platforms. This could include configuration
and compilation changes or changes in portability/compatibility.  However,
changes within modules for platforms should generally be listed in the
L</Modules and Pragmata> section.

=over 4

=item XXX-some-platform

XXX

=back

=head1 Internal Changes

XXX Changes which affect the interface available to C<XS> code go here.
Other significant internal changes for future core maintainers should
be noted as well.

[ List each change as a =item entry ]

=over 4

=item *

The C<SVf_AMAGIC> flag to indicate overloading is now on the stash, not the
object.  It is now set automatically whenever a method or @ISA changes, so
its meaning has changed, too.  It now means "potentially overloaded".  When
the overload table is calculated, the flag is automatically turned off if
there is no overloading, so there should be no noticeable slowdown.

The staleness of the overload tables is now checked when overload methods
are invoked, rather than during C<bless>.

"A" magic is gone.  The changes to the handling of the C<SVf_AMAGIC> flag
eliminate the need for it.

The core no longer increments C<PL_amagic_generation> (it doesn't need to).
But an XS module can still increment it to mark all overload tables as
stale.  (It is still not part of the API, though.)  Do not rely on this.
It may be deleted in the next release.

The fallback overload setting is now stored in its own stash entry, called
"(fallback".

=back

=head1 Selected Bug Fixes

XXX Important bug fixes in the core language are summarised here.
Bug fixes in files in F<ext/> and F<lib/> are best summarised in
L</Modules and Pragmata>.

[ List each fix as a =item entry ]

=over 4

=item *

C<goto ''> now looks for an empty label, producing the "goto must have
label" error message, instead of exiting the program [perl #111794].

=item *

C<goto "\0"> now dies with "Can't find label" instead of "goto must have
label".

=item *

The C function C<hv_store> used to result in crashes when used on C<%^H>
[perl #111000].

=item *

A call checker attached to a closure prototype via C<cv_set_call_checker>
is now copied to closures cloned from it.  So C<cv_set_call_checker> now
works inside an attribute handler for a closure.

=item *

Writing to C<$^N> used to have no effect.  Now it croaks with "Modification
of a read-only value" by default, but that can be overridden by a custom
regular expression engine, as with C<$1> [perl #112184].

=item *

C<undef> on a control character glob (C<undef *^H>) no longer emits an
erroneous warning about ambiguity [perl #112456].

=item *

For efficiency's sake, many operators and built-in functions return the
same scalar each time.  Lvalue subroutines and subroutines in the CORE::
namespace were allowing this implementation detail to leak through.
C<print &CORE::uc("a"), &CORE::uc("b")> used to print "BB".  The same thing
would happen with an lvalue subroutine returning the return value of C<uc>.
Now the value is copied in such cases.

=item *

C<method {}> syntax with an empty block or a block returning an empty list
used to crash or use some random value left on the stack as its invocant.
Now it produces an error.

=item *

C<vec> now works with extremely large offsets (>2 GB) [perl #111730].

=item *

Changes to overload settings now take effect immediately, as do changes to
inheritance that affect overloading.  They used to take effect only after
C<bless>.

Objects that were created before a class had any overloading used to remain
non-overloaded even if the class gained overloading through C<use overload>
or @ISA changes, and even after C<bless>.  This has been fixed
[perl #112708].

=back

=head1 Known Problems

XXX Descriptions of platform agnostic bugs we know we can't fix go here. Any
tests that had to be C<TODO>ed for the release would be noted here, unless
they were specific to a particular platform (see below).

This is a list of some significant unfixed bugs, which are regressions
from either 5.XXX.XXX or 5.XXX.XXX.

[ List each fix as a =item entry ]

=over 4

=item *

XXX

=back

=head1 Obituary

XXX If any significant core contributor has died, we've added a short obituary
here.

=head1 Acknowledgements

XXX Generate this with:

  perl Porting/acknowledgements.pl v5.16.0..HEAD

=head1 Reporting Bugs

If you find what you think is a bug, you might check the articles
recently posted to the comp.lang.perl.misc newsgroup and the perl
bug database at http://rt.perl.org/perlbug/ .  There may also be
information at http://www.perl.org/ , the Perl Home Page.

If you believe you have an unreported bug, please run the L<perlbug>
program included with your release.  Be sure to trim your bug down
to a tiny but sufficient test case.  Your bug report, along with the
output of C<perl -V>, will be sent off to perlbug@perl.org to be
analysed by the Perl porting team.

If the bug you are reporting has security implications, which make it
inappropriate to send to a publicly archived mailing list, then please send
it to perl5-security-report@perl.org. This points to a closed subscription
unarchived mailing list, which includes
all the core committers, who will be able
to help assess the impact of issues, figure out a resolution, and help
co-ordinate the release of patches to mitigate or fix the problem across all
platforms on which Perl is supported. Please only use this address for
security issues in the Perl core, not for modules independently
distributed on CPAN.

=head1 SEE ALSO

The F<Changes> file for an explanation of how to view exhaustive details
on what changed.

The F<INSTALL> file for how to build Perl.

The F<README> file for general stuff.

The F<Artistic> and F<Copying> files for copyright information.

=cut